16 Cygni-B

THE PLANET

The circle shows the location of the class G double star 16 Cygni
(in the constellation Cygnus). A small
telescope shows a pair of stars 39 seconds of arc apart. The
planet, one of the few to known to orbit within a binary system,
belongs to the fainter of the two, 16 Cygni-B. With a mass at
least 1.68 times that of Jupiter, the planet orbits 16 Cygni-B at
a distance that averages 1.68 astronomical units (12 percent
farther than Mars is from the Sun) with a period of 800 days, or
2.2 years. The orbit is quite eccentric, however; the planet comes
as close as 0.52 astronomical units to the star (72 percent Venus's
distance from the Sun) and then goes as far away as 2.8
astronomical units, a bit over half Jupiter's distance from the
Sun. From 16 Cygni-B's planet system (and no one knows if there
are any "earths"), the somewhat brighter component, 16 Cygni-A,
would shine with the brilliance of our full Moon.

THE STAR

16 Cygni is a fifth (5.32) magnitude star in the northwest corner
of Cygnus that is easily split in two with
a small amateur telescope to reveal two very sun-like stars 39
seconds of arc apart. The brighter, sixth magnitude (5.96)
component, which at 5750 Kelvin is only 30 degrees cooler than our
Sun, is about 60 percent more luminous as a
result the system's more advanced age of 8 billion years. The
fainter (sixth magnitude, 6.20), about which the planet revolves,
though at 5770 Kelvin (10 Kelvin cooler than the solar surface), is
also a bit (30 percent) brighter, implying from evolutionary theory
that each contains slightly more than a solar mass. Though no
orbit has been determined, it is clear that the stars are a pair,
as they are at the same distance and move through space together.
At minimum, they are 840 astronomical units apart, which would make
them take at least 17,000 years to go around each other.